/*
 * Copyright (c) 2021 - Manifold Systems LLC
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package manifold.ext.rt.proxy;

import java.io.ByteArrayOutputStream;
import java.io.DataOutputStream;
import java.io.File;
import java.io.IOException;
import java.io.OutputStream;
import java.lang.reflect.Array;
import java.lang.reflect.Method;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.ListIterator;
import java.util.Map;

import manifold.ext.rt.api.Structural;

/**
 * ProxyGenerator contains the code to generate a dynamic proxy class
 * for the java.lang.reflect.Proxy API.
 *
 * The external interfaces to ProxyGenerator is the static
 * "generateProxyClass" method.
 *
 * @author      Peter Jones
 * @since       1.3
 */
public class ProxyGenerator {
  /*
   * In the comments below, "JVMS" refers to The Java Virtual Machine
   * Specification Second Edition and "JLS" refers to the original
   * version of The Java Language Specification, unless otherwise
   * specified.
   */

  /* generate 1.5-era class file version */
  private static final int CLASSFILE_MAJOR_VERSION = 49;
  private static final int CLASSFILE_MINOR_VERSION = 0;

  /*
   * beginning of constants copied from
   * sun.tools.java.RuntimeConstants (which no longer exists):
   */

  /* constant pool tags */
  private static final int CONSTANT_UTF8              = 1;
  private static final int CONSTANT_UNICODE           = 2;
  private static final int CONSTANT_INTEGER           = 3;
  private static final int CONSTANT_FLOAT             = 4;
  private static final int CONSTANT_LONG              = 5;
  private static final int CONSTANT_DOUBLE            = 6;
  private static final int CONSTANT_CLASS             = 7;
  private static final int CONSTANT_STRING            = 8;
  private static final int CONSTANT_FIELD             = 9;
  private static final int CONSTANT_METHOD            = 10;
  private static final int CONSTANT_INTERFACEMETHOD   = 11;
  private static final int CONSTANT_NAMEANDTYPE       = 12;

  /* access and modifier flags */
  private static final int ACC_PUBLIC                 = 0x00000001;
  private static final int ACC_PRIVATE                = 0x00000002;
  //  private static final int ACC_PROTECTED              = 0x00000004;
  private static final int ACC_STATIC                 = 0x00000008;
  private static final int ACC_FINAL                  = 0x00000010;
  //  private static final int ACC_SYNCHRONIZED           = 0x00000020;
//  private static final int ACC_VOLATILE               = 0x00000040;
//  private static final int ACC_TRANSIENT              = 0x00000080;
//  private static final int ACC_NATIVE                 = 0x00000100;
//  private static final int ACC_INTERFACE              = 0x00000200;
//  private static final int ACC_ABSTRACT               = 0x00000400;
  private static final int ACC_SUPER                  = 0x00000020;
//  private static final int ACC_STRICT                 = 0x00000800;

  /* opcodes */
//  private static final int opc_nop                    = 0;
  private static final int opc_aconst_null            = 1;
  //  private static final int opc_iconst_m1              = 2;
  private static final int opc_iconst_0               = 3;
  //  private static final int opc_iconst_1               = 4;
//  private static final int opc_iconst_2               = 5;
//  private static final int opc_iconst_3               = 6;
//  private static final int opc_iconst_4               = 7;
//  private static final int opc_iconst_5               = 8;
//  private static final int opc_lconst_0               = 9;
//  private static final int opc_lconst_1               = 10;
//  private static final int opc_fconst_0               = 11;
//  private static final int opc_fconst_1               = 12;
//  private static final int opc_fconst_2               = 13;
//  private static final int opc_dconst_0               = 14;
//  private static final int opc_dconst_1               = 15;
  private static final int opc_bipush                 = 16;
  private static final int opc_sipush                 = 17;
  private static final int opc_ldc                    = 18;
  private static final int opc_ldc_w                  = 19;
  //  private static final int opc_ldc2_w                 = 20;
  private static final int opc_iload                  = 21;
  private static final int opc_lload                  = 22;
  private static final int opc_fload                  = 23;
  private static final int opc_dload                  = 24;
  private static final int opc_aload                  = 25;
  private static final int opc_iload_0                = 26;
  //  private static final int opc_iload_1                = 27;
//  private static final int opc_iload_2                = 28;
//  private static final int opc_iload_3                = 29;
  private static final int opc_lload_0                = 30;
  //  private static final int opc_lload_1                = 31;
//  private static final int opc_lload_2                = 32;
//  private static final int opc_lload_3                = 33;
  private static final int opc_fload_0                = 34;
  //  private static final int opc_fload_1                = 35;
//  private static final int opc_fload_2                = 36;
//  private static final int opc_fload_3                = 37;
  private static final int opc_dload_0                = 38;
  //  private static final int opc_dload_1                = 39;
//  private static final int opc_dload_2                = 40;
//  private static final int opc_dload_3                = 41;
  private static final int opc_aload_0                = 42;
  //  private static final int opc_aload_1                = 43;
//  private static final int opc_aload_2                = 44;
//  private static final int opc_aload_3                = 45;
//  private static final int opc_iaload                 = 46;
//  private static final int opc_laload                 = 47;
//  private static final int opc_faload                 = 48;
//  private static final int opc_daload                 = 49;
//  private static final int opc_aaload                 = 50;
//  private static final int opc_baload                 = 51;
//  private static final int opc_caload                 = 52;
//  private static final int opc_saload                 = 53;
//  private static final int opc_istore                 = 54;
//  private static final int opc_lstore                 = 55;
//  private static final int opc_fstore                 = 56;
//  private static final int opc_dstore                 = 57;
  private static final int opc_astore                 = 58;
  //  private static final int opc_istore_0               = 59;
//  private static final int opc_istore_1               = 60;
//  private static final int opc_istore_2               = 61;
//  private static final int opc_istore_3               = 62;
//  private static final int opc_lstore_0               = 63;
//  private static final int opc_lstore_1               = 64;
//  private static final int opc_lstore_2               = 65;
//  private static final int opc_lstore_3               = 66;
//  private static final int opc_fstore_0               = 67;
//  private static final int opc_fstore_1               = 68;
//  private static final int opc_fstore_2               = 69;
//  private static final int opc_fstore_3               = 70;
//  private static final int opc_dstore_0               = 71;
//  private static final int opc_dstore_1               = 72;
//  private static final int opc_dstore_2               = 73;
//  private static final int opc_dstore_3               = 74;
  private static final int opc_astore_0               = 75;
  //  private static final int opc_astore_1               = 76;
//  private static final int opc_astore_2               = 77;
//  private static final int opc_astore_3               = 78;
//  private static final int opc_iastore                = 79;
//  private static final int opc_lastore                = 80;
//  private static final int opc_fastore                = 81;
//  private static final int opc_dastore                = 82;
  private static final int opc_aastore                = 83;
  //  private static final int opc_bastore                = 84;
//  private static final int opc_castore                = 85;
//  private static final int opc_sastore                = 86;
  private static final int opc_pop                    = 87;
  //  private static final int opc_pop2                   = 88;
  private static final int opc_dup                    = 89;
  //  private static final int opc_dup_x1                 = 90;
//  private static final int opc_dup_x2                 = 91;
//  private static final int opc_dup2                   = 92;
//  private static final int opc_dup2_x1                = 93;
//  private static final int opc_dup2_x2                = 94;
//  private static final int opc_swap                   = 95;
//  private static final int opc_iadd                   = 96;
//  private static final int opc_ladd                   = 97;
//  private static final int opc_fadd                   = 98;
//  private static final int opc_dadd                   = 99;
//  private static final int opc_isub                   = 100;
//  private static final int opc_lsub                   = 101;
//  private static final int opc_fsub                   = 102;
//  private static final int opc_dsub                   = 103;
//  private static final int opc_imul                   = 104;
//  private static final int opc_lmul                   = 105;
//  private static final int opc_fmul                   = 106;
//  private static final int opc_dmul                   = 107;
//  private static final int opc_idiv                   = 108;
//  private static final int opc_ldiv                   = 109;
//  private static final int opc_fdiv                   = 110;
//  private static final int opc_ddiv                   = 111;
//  private static final int opc_irem                   = 112;
//  private static final int opc_lrem                   = 113;
//  private static final int opc_frem                   = 114;
//  private static final int opc_drem                   = 115;
//  private static final int opc_ineg                   = 116;
//  private static final int opc_lneg                   = 117;
//  private static final int opc_fneg                   = 118;
//  private static final int opc_dneg                   = 119;
//  private static final int opc_ishl                   = 120;
//  private static final int opc_lshl                   = 121;
//  private static final int opc_ishr                   = 122;
//  private static final int opc_lshr                   = 123;
//  private static final int opc_iushr                  = 124;
//  private static final int opc_lushr                  = 125;
//  private static final int opc_iand                   = 126;
//  private static final int opc_land                   = 127;
//  private static final int opc_ior                    = 128;
//  private static final int opc_lor                    = 129;
//  private static final int opc_ixor                   = 130;
//  private static final int opc_lxor                   = 131;
//  private static final int opc_iinc                   = 132;
//  private static final int opc_i2l                    = 133;
//  private static final int opc_i2f                    = 134;
//  private static final int opc_i2d                    = 135;
//  private static final int opc_l2i                    = 136;
//  private static final int opc_l2f                    = 137;
//  private static final int opc_l2d                    = 138;
//  private static final int opc_f2i                    = 139;
//  private static final int opc_f2l                    = 140;
//  private static final int opc_f2d                    = 141;
//  private static final int opc_d2i                    = 142;
//  private static final int opc_d2l                    = 143;
//  private static final int opc_d2f                    = 144;
//  private static final int opc_i2b                    = 145;
//  private static final int opc_i2c                    = 146;
//  private static final int opc_i2s                    = 147;
//  private static final int opc_lcmp                   = 148;
//  private static final int opc_fcmpl                  = 149;
//  private static final int opc_fcmpg                  = 150;
//  private static final int opc_dcmpl                  = 151;
//  private static final int opc_dcmpg                  = 152;
//  private static final int opc_ifeq                   = 153;
//  private static final int opc_ifne                   = 154;
//  private static final int opc_iflt                   = 155;
//  private static final int opc_ifge                   = 156;
//  private static final int opc_ifgt                   = 157;
//  private static final int opc_ifle                   = 158;
//  private static final int opc_if_icmpeq              = 159;
//  private static final int opc_if_icmpne              = 160;
//  private static final int opc_if_icmplt              = 161;
//  private static final int opc_if_icmpge              = 162;
//  private static final int opc_if_icmpgt              = 163;
//  private static final int opc_if_icmple              = 164;
//  private static final int opc_if_acmpeq              = 165;
//  private static final int opc_if_acmpne              = 166;
//  private static final int opc_goto                   = 167;
//  private static final int opc_jsr                    = 168;
//  private static final int opc_ret                    = 169;
//  private static final int opc_tableswitch            = 170;
//  private static final int opc_lookupswitch           = 171;
  private static final int opc_ireturn                = 172;
  private static final int opc_lreturn                = 173;
  private static final int opc_freturn                = 174;
  private static final int opc_dreturn                = 175;
  private static final int opc_areturn                = 176;
  private static final int opc_return                 = 177;
  private static final int opc_getstatic              = 178;
  private static final int opc_putstatic              = 179;
  private static final int opc_getfield               = 180;
  //  private static final int opc_putfield               = 181;
  private static final int opc_invokevirtual          = 182;
  private static final int opc_invokespecial          = 183;
  private static final int opc_invokestatic           = 184;
  private static final int opc_invokeinterface        = 185;
  private static final int opc_new                    = 187;
  //  private static final int opc_newarray               = 188;
  private static final int opc_anewarray              = 189;
  //  private static final int opc_arraylength            = 190;
  private static final int opc_athrow                 = 191;
  private static final int opc_checkcast              = 192;
  //  private static final int opc_instanceof             = 193;
//  private static final int opc_monitorenter           = 194;
//  private static final int opc_monitorexit            = 195;
  private static final int opc_wide                   = 196;
//  private static final int opc_multianewarray         = 197;
//  private static final int opc_ifnull                 = 198;
//  private static final int opc_ifnonnull              = 199;
//  private static final int opc_goto_w                 = 200;
//  private static final int opc_jsr_w                  = 201;

  // end of constants copied from sun.tools.java.RuntimeConstants

  /** name of the superclass of proxy classes */
  private final static String superclassName = "java/lang/reflect/Proxy";

  /** name of field for storing a proxy instance's invocation handler */
  private final static String handlerFieldName = "h";

  public static final boolean saveGeneratedFiles = false;
//  /** debugging flag for saving generated class files */
//  private final static boolean saveGeneratedFiles =
//    java.security.AccessController.doPrivileged(
//      new GetBooleanAction(
//        "ProxyGenerator.saveGeneratedFiles")).booleanValue();

  /**
   * Generate a public proxy class given a name and a list of proxy interfaces.
   */
  public static byte[] generateProxyClass(final String name,
                                          Class<?>[] interfaces) {
    return generateProxyClass(name, interfaces, (ACC_PUBLIC | ACC_FINAL | ACC_SUPER));
  }

  /**
   * Generate a proxy class given a name and a list of proxy interfaces.
   *
   * @param name        the class name of the proxy class
   * @param interfaces  proxy interfaces
   * @param accessFlags access flags of the proxy class
   */
  public static byte[] generateProxyClass(final String name,
                                          Class<?>[] interfaces,
                                          int accessFlags)
  {
    ProxyGenerator gen = new ProxyGenerator(name, interfaces, accessFlags);
    final byte[] classFile = gen.generateClassFile();

    if ( saveGeneratedFiles ) {
      java.security.AccessController.doPrivileged(
        new java.security.PrivilegedAction<Void>() {
          public Void run() {
            try {
              int i = name.lastIndexOf('.');
              Path path;
              if (i > 0) {
                Path dir = Paths.get(name.substring(0, i).replace('.', File.separatorChar));
                Files.createDirectories(dir);
                path = dir.resolve(name.substring(i+1, name.length()) + ".class");
              } else {
                path = Paths.get(name + ".class");
              }
              Files.write(path, classFile);
              return null;
            } catch (IOException e) {
              throw new InternalError(
                "I/O exception saving generated file: " + e);
            }
          }
        });
    }

    return classFile;
  }

  /* preloaded Method objects for methods in java.lang.Object */
  private static Method hashCodeMethod;
  private static Method equalsMethod;
  private static Method toStringMethod;
  static {
    try {
      hashCodeMethod = Object.class.getMethod("hashCode");
      equalsMethod =
        Object.class.getMethod("equals", new Class<?>[] { Object.class });
      toStringMethod = Object.class.getMethod("toString");
    } catch (NoSuchMethodException e) {
      throw new NoSuchMethodError(e.getMessage());
    }
  }

  /** name of proxy class */
  private String className;

  /** proxy interfaces */
  private Class<?>[] interfaces;

  /** proxy class access flags */
  private int accessFlags;

  /** constant pool of class being generated */
  private ProxyGenerator.ConstantPool cp = new ProxyGenerator.ConstantPool();

  /** FieldInfo struct for each field of generated class */
  private List<ProxyGenerator.FieldInfo> fields = new ArrayList<>();

  /** MethodInfo struct for each method of generated class */
  private List<ProxyGenerator.MethodInfo> methods = new ArrayList<>();

  /**
   * maps method signature string to list of ProxyMethod objects for
   * proxy methods with that signature
   */
  private Map<String, List<ProxyGenerator.ProxyMethod>> proxyMethods = new HashMap<>();

  /** count of ProxyMethod objects added to proxyMethods */
  private int proxyMethodCount = 0;

  /**
   * Construct a ProxyGenerator to generate a proxy class with the
   * specified name and for the given interfaces.
   *
   * A ProxyGenerator object contains the state for the ongoing
   * generation of a particular proxy class.
   */
  private ProxyGenerator(String className, Class<?>[] interfaces, int accessFlags) {
    this.className = className;
    this.interfaces = interfaces;
    this.accessFlags = accessFlags;
  }

  /**
   * Generate a class file for the proxy class.  This method drives the
   * class file generation process.
   */
  private byte[] generateClassFile() {

    /* ============================================================
     * Step 1: Assemble ProxyMethod objects for all methods to
     * generate proxy dispatching code for.
     */

    /*
     * Record that proxy methods are needed for the hashCode, equals,
     * and toString methods of java.lang.Object.  This is done before
     * the methods from the proxy interfaces so that the methods from
     * java.lang.Object take precedence over duplicate methods in the
     * proxy interfaces.
     */
    addProxyMethod(hashCodeMethod, Object.class);
    addProxyMethod(equalsMethod, Object.class);
    addProxyMethod(toStringMethod, Object.class);

    /*
     * Now record all of the methods from the proxy interfaces, giving
     * earlier interfaces precedence over later ones with duplicate
     * methods.
     */
    for (Class<?> intf : interfaces) {
      for (Method m : intf.getMethods()) {
        addProxyMethod(m, intf);
      }
    }

    /*
     * For each set of proxy methods with the same signature,
     * verify that the methods' return types are compatible.
     */
    for (List<ProxyGenerator.ProxyMethod> sigmethods : proxyMethods.values()) {
      checkReturnTypes(sigmethods);
    }

    /* ============================================================
     * Step 2: Assemble FieldInfo and MethodInfo structs for all of
     * fields and methods in the class we are generating.
     */
    try {
      methods.add(generateConstructor());

      for (List<ProxyGenerator.ProxyMethod> sigmethods : proxyMethods.values()) {
        for ( ProxyGenerator.ProxyMethod pm : sigmethods) {

          // add static field for method's Method object
          fields.add(new ProxyGenerator.FieldInfo(pm.methodFieldName,
            "Ljava/lang/reflect/Method;",
            ACC_PRIVATE | ACC_STATIC));

          // generate code for proxy method and add it
          methods.add(pm.generateMethod());
        }
      }

      methods.add(generateStaticInitializer());

    } catch (IOException e) {
      throw new InternalError("unexpected I/O Exception", e);
    }

    if (methods.size() > 65535) {
      throw new IllegalArgumentException("method limit exceeded");
    }
    if (fields.size() > 65535) {
      throw new IllegalArgumentException("field limit exceeded");
    }

    /* ============================================================
     * Step 3: Write the final class file.
     */

    /*
     * Make sure that constant pool indexes are reserved for the
     * following items before starting to write the final class file.
     */
    cp.getClass(dotToSlash(className));
    cp.getClass(superclassName);
    for (Class<?> intf: interfaces) {
      cp.getClass(dotToSlash(intf.getName()));
    }

    /*
     * Disallow new constant pool additions beyond this point, since
     * we are about to write the final constant pool table.
     */
    cp.setReadOnly();

    ByteArrayOutputStream bout = new ByteArrayOutputStream();
    DataOutputStream dout = new DataOutputStream(bout);

    try {
      /*
       * Write all the items of the "ClassFile" structure.
       * See JVMS section 4.1.
       */
      // u4 magic;
      dout.writeInt(0xCAFEBABE);
      // u2 minor_version;
      dout.writeShort(CLASSFILE_MINOR_VERSION);
      // u2 major_version;
      dout.writeShort(CLASSFILE_MAJOR_VERSION);

      cp.write(dout);             // (write constant pool)

      // u2 access_flags;
      dout.writeShort(accessFlags);
      // u2 this_class;
      dout.writeShort(cp.getClass(dotToSlash(className)));
      // u2 super_class;
      dout.writeShort(cp.getClass(superclassName));

      // u2 interfaces_count;
      dout.writeShort(interfaces.length);
      // u2 interfaces[interfaces_count];
      for (Class<?> intf : interfaces) {
        dout.writeShort(cp.getClass(
          dotToSlash(intf.getName())));
      }

      // u2 fields_count;
      dout.writeShort(fields.size());
      // field_info fields[fields_count];
      for ( ProxyGenerator.FieldInfo f : fields) {
        f.write(dout);
      }

      // u2 methods_count;
      dout.writeShort(methods.size());
      // method_info methods[methods_count];
      for ( ProxyGenerator.MethodInfo m : methods) {
        m.write(dout);
      }

      // u2 attributes_count;
      dout.writeShort(0); // (no ClassFile attributes for proxy classes)

    } catch (IOException e) {
      throw new InternalError("unexpected I/O Exception", e);
    }

    return bout.toByteArray();
  }

  /**
   * Add another method to be proxied, either by creating a new
   * ProxyMethod object or augmenting an old one for a duplicate
   * method.
   *
   * "fromClass" indicates the proxy interface that the method was
   * found through, which may be different from (a subinterface of)
   * the method's "declaring class".  Note that the first Method
   * object passed for a given name and descriptor identifies the
   * Method object (and thus the declaring class) that will be
   * passed to the invocation handler's "invoke" method for a given
   * set of duplicate methods.
   */
  private void addProxyMethod(Method m, Class<?> fromClass) {
    String name = m.getName();
    Class<?>[] parameterTypes = m.getParameterTypes();
    Class<?> returnType = m.getReturnType();
    Class<?>[] exceptionTypes = m.getExceptionTypes();

    String sig = name + getParameterDescriptors(parameterTypes);
    List<ProxyGenerator.ProxyMethod> sigmethods = proxyMethods.get(sig);
    if (sigmethods != null) {
      for ( ProxyGenerator.ProxyMethod pm : sigmethods) {
        if (returnType == pm.returnType) {
          /*
           * Found a match: reduce exception types to the
           * greatest set of exceptions that can thrown
           * compatibly with the throws clauses of both
           * overridden methods.
           */
          List<Class<?>> legalExceptions = new ArrayList<>();
          collectCompatibleTypes(
            exceptionTypes, pm.exceptionTypes, legalExceptions);
          collectCompatibleTypes(
            pm.exceptionTypes, exceptionTypes, legalExceptions);
          pm.exceptionTypes = new Class<?>[legalExceptions.size()];
          pm.exceptionTypes =
            legalExceptions.toArray(pm.exceptionTypes);
          return;
        }
      }
    } else {
      sigmethods = new ArrayList<>(3);
      proxyMethods.put(sig, sigmethods);
    }
    sigmethods.add(new ProxyGenerator.ProxyMethod(name, parameterTypes, returnType,
      exceptionTypes, fromClass));
  }

  /**
   * For a given set of proxy methods with the same signature, check
   * that their return types are compatible according to the Proxy
   * specification.
   *
   * Specifically, if there is more than one such method, then all
   * of the return types must be reference types, and there must be
   * one return type that is assignable to each of the rest of them.
   */
  private static void checkReturnTypes(List<ProxyGenerator.ProxyMethod> methods) {
    /*
     * If there is only one method with a given signature, there
     * cannot be a conflict.  This is the only case in which a
     * primitive (or void) return type is allowed.
     */
    if (methods.size() < 2) {
      return;
    }

    /*
     * List of return types that are not yet known to be
     * assignable from ("covered" by) any of the others.
     */
    LinkedList<Class<?>> uncoveredReturnTypes = new LinkedList<>();

    nextNewReturnType:
    for ( ProxyGenerator.ProxyMethod pm : methods) {
      Class<?> newReturnType = pm.returnType;
      if (newReturnType.isPrimitive()) {
        throw new IllegalArgumentException(
          "methods with same signature " +
            getFriendlyMethodSignature(pm.methodName,
              pm.parameterTypes) +
            " but incompatible return types: " +
            newReturnType.getName() + " and others");
      }
      boolean added = false;

      /*
       * Compare the new return type to the existing uncovered
       * return types.
       */
      ListIterator<Class<?>> liter = uncoveredReturnTypes.listIterator();
      while (liter.hasNext()) {
        Class<?> uncoveredReturnType = liter.next();

        /*
         * If an existing uncovered return type is assignable
         * to this new one, then we can forget the new one.
         */
        if (newReturnType.isAssignableFrom(uncoveredReturnType)) {
          assert !added;
          continue nextNewReturnType;
        }

        /*
         * If the new return type is assignable to an existing
         * uncovered one, then should replace the existing one
         * with the new one (or just forget the existing one,
         * if the new one has already be put in the list).
         */
        if (uncoveredReturnType.isAssignableFrom(newReturnType)) {
          // (we can assume that each return type is unique)
          if (!added) {
            liter.set(newReturnType);
            added = true;
          } else {
            liter.remove();
          }
        }
      }

      /*
       * If we got through the list of existing uncovered return
       * types without an assignability relationship, then add
       * the new return type to the list of uncovered ones.
       */
      if (!added) {
        uncoveredReturnTypes.add(newReturnType);
      }
    }

    /*
     * We shouldn't end up with more than one return type that is
     * not assignable from any of the others.
     */
    if (uncoveredReturnTypes.size() > 1) {
      ProxyGenerator.ProxyMethod pm = methods.get(0);
      throw new IllegalArgumentException(
        "methods with same signature " +
          getFriendlyMethodSignature(pm.methodName, pm.parameterTypes) +
          " but incompatible return types: " + uncoveredReturnTypes);
    }
  }

  /**
   * A FieldInfo object contains information about a particular field
   * in the class being generated.  The class mirrors the data items of
   * the "field_info" structure of the class file format (see JVMS 4.5).
   */
  private class FieldInfo {
    public int accessFlags;
    public String name;
    public String descriptor;

    public FieldInfo(String name, String descriptor, int accessFlags) {
      this.name = name;
      this.descriptor = descriptor;
      this.accessFlags = accessFlags;

      /*
       * Make sure that constant pool indexes are reserved for the
       * following items before starting to write the final class file.
       */
      cp.getUtf8(name);
      cp.getUtf8(descriptor);
    }

    public void write(DataOutputStream out) throws IOException {
      /*
       * Write all the items of the "field_info" structure.
       * See JVMS section 4.5.
       */
      // u2 access_flags;
      out.writeShort(accessFlags);
      // u2 name_index;
      out.writeShort(cp.getUtf8(name));
      // u2 descriptor_index;
      out.writeShort(cp.getUtf8(descriptor));
      // u2 attributes_count;
      out.writeShort(0);  // (no field_info attributes for proxy classes)
    }
  }

  /**
   * An ExceptionTableEntry object holds values for the data items of
   * an entry in the "exception_table" item of the "Code" attribute of
   * "method_info" structures (see JVMS 4.7.3).
   */
  private static class ExceptionTableEntry {
    public short startPc;
    public short endPc;
    public short handlerPc;
    public short catchType;

    public ExceptionTableEntry(short startPc, short endPc,
                               short handlerPc, short catchType)
    {
      this.startPc = startPc;
      this.endPc = endPc;
      this.handlerPc = handlerPc;
      this.catchType = catchType;
    }
  };

  /**
   * A MethodInfo object contains information about a particular method
   * in the class being generated.  This class mirrors the data items of
   * the "method_info" structure of the class file format (see JVMS 4.6).
   */
  private class MethodInfo {
    public int accessFlags;
    public String name;
    public String descriptor;
    public short maxStack;
    public short maxLocals;
    public ByteArrayOutputStream code = new ByteArrayOutputStream();
    public List<ProxyGenerator.ExceptionTableEntry> exceptionTable =
      new ArrayList<ProxyGenerator.ExceptionTableEntry>();
    public short[] declaredExceptions;

    public MethodInfo(String name, String descriptor, int accessFlags) {
      this.name = name;
      this.descriptor = descriptor;
      this.accessFlags = accessFlags;

      /*
       * Make sure that constant pool indexes are reserved for the
       * following items before starting to write the final class file.
       */
      cp.getUtf8(name);
      cp.getUtf8(descriptor);
      cp.getUtf8("Code");
      cp.getUtf8("Exceptions");
    }

    public void write(DataOutputStream out) throws IOException {
      /*
       * Write all the items of the "method_info" structure.
       * See JVMS section 4.6.
       */
      // u2 access_flags;
      out.writeShort(accessFlags);
      // u2 name_index;
      out.writeShort(cp.getUtf8(name));
      // u2 descriptor_index;
      out.writeShort(cp.getUtf8(descriptor));
      // u2 attributes_count;
      out.writeShort(2);  // (two method_info attributes:)

      // Write "Code" attribute. See JVMS section 4.7.3.

      // u2 attribute_name_index;
      out.writeShort(cp.getUtf8("Code"));
      // u4 attribute_length;
      out.writeInt(12 + code.size() + 8 * exceptionTable.size());
      // u2 max_stack;
      out.writeShort(maxStack);
      // u2 max_locals;
      out.writeShort(maxLocals);
      // u2 code_length;
      out.writeInt(code.size());
      // u1 code[code_length];
      code.writeTo(out);
      // u2 exception_table_length;
      out.writeShort(exceptionTable.size());
      for ( ProxyGenerator.ExceptionTableEntry e : exceptionTable) {
        // u2 start_pc;
        out.writeShort(e.startPc);
        // u2 end_pc;
        out.writeShort(e.endPc);
        // u2 handler_pc;
        out.writeShort(e.handlerPc);
        // u2 catch_type;
        out.writeShort(e.catchType);
      }
      // u2 attributes_count;
      out.writeShort(0);

      // write "Exceptions" attribute.  See JVMS section 4.7.4.

      // u2 attribute_name_index;
      out.writeShort(cp.getUtf8("Exceptions"));
      // u4 attributes_length;
      out.writeInt(2 + 2 * declaredExceptions.length);
      // u2 number_of_exceptions;
      out.writeShort(declaredExceptions.length);
      // u2 exception_index_table[number_of_exceptions];
      for (short value : declaredExceptions) {
        out.writeShort(value);
      }
    }

  }

  /**
   * A ProxyMethod object represents a proxy method in the proxy class
   * being generated: a method whose implementation will encode and
   * dispatch invocations to the proxy instance's invocation handler.
   */
  private class ProxyMethod {

    public String methodName;
    public Class<?>[] parameterTypes;
    public Class<?> returnType;
    public Class<?>[] exceptionTypes;
    public Class<?> fromClass;
    public String methodFieldName;

    private ProxyMethod(String methodName, Class<?>[] parameterTypes,
                        Class<?> returnType, Class<?>[] exceptionTypes,
                        Class<?> fromClass)
    {
      this.methodName = methodName;
      this.parameterTypes = parameterTypes;
      this.returnType = returnType;
      this.exceptionTypes = exceptionTypes;
      this.fromClass = fromClass;
      this.methodFieldName = "m" + proxyMethodCount++;
    }

    /**
     * Return a MethodInfo object for this method, including generating
     * the code and exception table entry.
     */
    private ProxyGenerator.MethodInfo generateMethod() throws IOException {
      String desc = getMethodDescriptor(parameterTypes, returnType);
      ProxyGenerator.MethodInfo minfo = new ProxyGenerator.MethodInfo(methodName, desc,
        ACC_PUBLIC | ACC_FINAL);

      int[] parameterSlot = new int[parameterTypes.length];
      int nextSlot = 1;
      for (int i = 0; i < parameterSlot.length; i++) {
        parameterSlot[i] = nextSlot;
        nextSlot += getWordsPerType(parameterTypes[i]);
      }
      int localSlot0 = nextSlot;
      short pc, tryBegin = 0, tryEnd;

      DataOutputStream out = new DataOutputStream(minfo.code);

      code_aload(0, out);

      out.writeByte(opc_getfield);
      out.writeShort(cp.getFieldRef(
        superclassName,
        handlerFieldName, "Ljava/lang/reflect/InvocationHandler;"));

      code_aload(0, out);

      out.writeByte(opc_getstatic);
      out.writeShort(cp.getFieldRef(
        dotToSlash(className),
        methodFieldName, "Ljava/lang/reflect/Method;"));

      if (parameterTypes.length > 0) {

        code_ipush(parameterTypes.length, out);

        out.writeByte(opc_anewarray);
        out.writeShort(cp.getClass("java/lang/Object"));

        for (int i = 0; i < parameterTypes.length; i++) {

          out.writeByte(opc_dup);

          code_ipush(i, out);

          codeWrapArgument(parameterTypes[i], parameterSlot[i], out);

          out.writeByte(opc_aastore);
        }
      } else {

        out.writeByte(opc_aconst_null);
      }

      out.writeByte(opc_invokeinterface);
      out.writeShort(cp.getInterfaceMethodRef(
        "java/lang/reflect/InvocationHandler",
        "invoke",
        "(Ljava/lang/Object;Ljava/lang/reflect/Method;" +
          "[Ljava/lang/Object;)Ljava/lang/Object;"));
      out.writeByte(4);
      out.writeByte(0);

      if (returnType == void.class) {

        out.writeByte(opc_pop);

        out.writeByte(opc_return);

      } else {

        codeUnwrapReturnValue(returnType, out);
      }

      tryEnd = pc = (short) minfo.code.size();

      List<Class<?>> catchList = computeUniqueCatchList(exceptionTypes);
      if (catchList.size() > 0) {

        for (Class<?> ex : catchList) {
          minfo.exceptionTable.add(new ProxyGenerator.ExceptionTableEntry(
            tryBegin, tryEnd, pc,
            cp.getClass(dotToSlash(ex.getName()))));
        }

        out.writeByte(opc_athrow);

        pc = (short) minfo.code.size();

        minfo.exceptionTable.add(new ProxyGenerator.ExceptionTableEntry(
          tryBegin, tryEnd, pc, cp.getClass("java/lang/Throwable")));

        code_astore(localSlot0, out);

        out.writeByte(opc_new);
        out.writeShort(cp.getClass(
          "java/lang/reflect/UndeclaredThrowableException"));

        out.writeByte(opc_dup);

        code_aload(localSlot0, out);

        out.writeByte(opc_invokespecial);

        out.writeShort(cp.getMethodRef(
          "java/lang/reflect/UndeclaredThrowableException",
          "<init>", "(Ljava/lang/Throwable;)V"));

        out.writeByte(opc_athrow);
      }

      if (minfo.code.size() > 65535) {
        throw new IllegalArgumentException("code size limit exceeded");
      }

      minfo.maxStack = 10;
      minfo.maxLocals = (short) (localSlot0 + 1);
      minfo.declaredExceptions = new short[exceptionTypes.length];
      for (int i = 0; i < exceptionTypes.length; i++) {
        minfo.declaredExceptions[i] = cp.getClass(
          dotToSlash(exceptionTypes[i].getName()));
      }

      return minfo;
    }

    /**
     * Generate code for wrapping an argument of the given type
     * whose value can be found at the specified local variable
     * index, in order for it to be passed (as an Object) to the
     * invocation handler's "invoke" method.  The code is written
     * to the supplied stream.
     */
    private void codeWrapArgument(Class<?> type, int slot,
                                  DataOutputStream out)
      throws IOException
    {
      if (type.isPrimitive()) {
        ProxyGenerator.PrimitiveTypeInfo prim = ProxyGenerator.PrimitiveTypeInfo.get(type);

        if (type == int.class ||
          type == boolean.class ||
          type == byte.class ||
          type == char.class ||
          type == short.class)
        {
          code_iload(slot, out);
        } else if (type == long.class) {
          code_lload(slot, out);
        } else if (type == float.class) {
          code_fload(slot, out);
        } else if (type == double.class) {
          code_dload(slot, out);
        } else {
          throw new AssertionError();
        }

        out.writeByte(opc_invokestatic);
        out.writeShort(cp.getMethodRef(
          prim.wrapperClassName,
          "valueOf", prim.wrapperValueOfDesc));

      } else {

        code_aload(slot, out);
      }
    }

    /**
     * Generate code for unwrapping a return value of the given
     * type from the invocation handler's "invoke" method (as type
     * Object) to its correct type.  The code is written to the
     * supplied stream.
     */
    private void codeUnwrapReturnValue(Class<?> type, DataOutputStream out)
      throws IOException
    {
      if (type.isPrimitive()) {
        ProxyGenerator.PrimitiveTypeInfo prim = ProxyGenerator.PrimitiveTypeInfo.get(type);

        out.writeByte(opc_checkcast);
        out.writeShort(cp.getClass(prim.wrapperClassName));

        out.writeByte(opc_invokevirtual);
        out.writeShort(cp.getMethodRef(
          prim.wrapperClassName,
          prim.unwrapMethodName, prim.unwrapMethodDesc));

        if (type == int.class ||
          type == boolean.class ||
          type == byte.class ||
          type == char.class ||
          type == short.class)
        {
          out.writeByte(opc_ireturn);
        } else if (type == long.class) {
          out.writeByte(opc_lreturn);
        } else if (type == float.class) {
          out.writeByte(opc_freturn);
        } else if (type == double.class) {
          out.writeByte(opc_dreturn);
        } else {
          throw new AssertionError();
        }

      } else {

        Structural structural = type.getAnnotation( Structural.class );
        if( structural == null )
        {
          out.writeByte( opc_checkcast );
          out.writeShort( cp.getClass( dotToSlash( type.getName() ) ) );
        }
        out.writeByte(opc_areturn);
      }
    }

    /**
     * Generate code for initializing the static field that stores
     * the Method object for this proxy method.  The code is written
     * to the supplied stream.
     */
    private void codeFieldInitialization(DataOutputStream out)
      throws IOException
    {
      codeClassForName(fromClass, out);

      code_ldc(cp.getString(methodName), out);

      code_ipush(parameterTypes.length, out);

      out.writeByte(opc_anewarray);
      out.writeShort(cp.getClass("java/lang/Class"));

      for (int i = 0; i < parameterTypes.length; i++) {

        out.writeByte(opc_dup);

        code_ipush(i, out);

        if (parameterTypes[i].isPrimitive()) {
          ProxyGenerator.PrimitiveTypeInfo prim =
            ProxyGenerator.PrimitiveTypeInfo.get(parameterTypes[i]);

          out.writeByte(opc_getstatic);
          out.writeShort(cp.getFieldRef(
            prim.wrapperClassName, "TYPE", "Ljava/lang/Class;"));

        } else {
          codeClassForName(parameterTypes[i], out);
        }

        out.writeByte(opc_aastore);
      }

      out.writeByte(opc_invokevirtual);
      out.writeShort(cp.getMethodRef(
        "java/lang/Class",
        "getMethod",
        "(Ljava/lang/String;[Ljava/lang/Class;)" +
          "Ljava/lang/reflect/Method;"));

      out.writeByte(opc_putstatic);
      out.writeShort(cp.getFieldRef(
        dotToSlash(className),
        methodFieldName, "Ljava/lang/reflect/Method;"));
    }
  }

  /**
   * Generate the constructor method for the proxy class.
   */
  private ProxyGenerator.MethodInfo generateConstructor() throws IOException {
    ProxyGenerator.MethodInfo minfo = new ProxyGenerator.MethodInfo(
      "<init>", "(Ljava/lang/reflect/InvocationHandler;)V",
      ACC_PUBLIC);

    DataOutputStream out = new DataOutputStream(minfo.code);

    code_aload(0, out);

    code_aload(1, out);

    out.writeByte(opc_invokespecial);
    out.writeShort(cp.getMethodRef(
      superclassName,
      "<init>", "(Ljava/lang/reflect/InvocationHandler;)V"));

    out.writeByte(opc_return);

    minfo.maxStack = 10;
    minfo.maxLocals = 2;
    minfo.declaredExceptions = new short[0];

    return minfo;
  }

  /**
   * Generate the static initializer method for the proxy class.
   */
  private ProxyGenerator.MethodInfo generateStaticInitializer() throws IOException {
    ProxyGenerator.MethodInfo minfo = new ProxyGenerator.MethodInfo(
      "<clinit>", "()V", ACC_STATIC);

    int localSlot0 = 1;
    short pc, tryBegin = 0, tryEnd;

    DataOutputStream out = new DataOutputStream(minfo.code);

    for (List<ProxyGenerator.ProxyMethod> sigmethods : proxyMethods.values()) {
      for ( ProxyGenerator.ProxyMethod pm : sigmethods) {
        pm.codeFieldInitialization(out);
      }
    }

    out.writeByte(opc_return);

    tryEnd = pc = (short) minfo.code.size();

    minfo.exceptionTable.add(new ProxyGenerator.ExceptionTableEntry(
      tryBegin, tryEnd, pc,
      cp.getClass("java/lang/NoSuchMethodException")));

    code_astore(localSlot0, out);

    out.writeByte(opc_new);
    out.writeShort(cp.getClass("java/lang/NoSuchMethodError"));

    out.writeByte(opc_dup);

    code_aload(localSlot0, out);

    out.writeByte(opc_invokevirtual);
    out.writeShort(cp.getMethodRef(
      "java/lang/Throwable", "getMessage", "()Ljava/lang/String;"));

    out.writeByte(opc_invokespecial);
    out.writeShort(cp.getMethodRef(
      "java/lang/NoSuchMethodError", "<init>", "(Ljava/lang/String;)V"));

    out.writeByte(opc_athrow);

    pc = (short) minfo.code.size();

    minfo.exceptionTable.add(new ProxyGenerator.ExceptionTableEntry(
      tryBegin, tryEnd, pc,
      cp.getClass("java/lang/ClassNotFoundException")));

    code_astore(localSlot0, out);

    out.writeByte(opc_new);
    out.writeShort(cp.getClass("java/lang/NoClassDefFoundError"));

    out.writeByte(opc_dup);

    code_aload(localSlot0, out);

    out.writeByte(opc_invokevirtual);
    out.writeShort(cp.getMethodRef(
      "java/lang/Throwable", "getMessage", "()Ljava/lang/String;"));

    out.writeByte(opc_invokespecial);
    out.writeShort(cp.getMethodRef(
      "java/lang/NoClassDefFoundError",
      "<init>", "(Ljava/lang/String;)V"));

    out.writeByte(opc_athrow);

    if (minfo.code.size() > 65535) {
      throw new IllegalArgumentException("code size limit exceeded");
    }

    minfo.maxStack = 10;
    minfo.maxLocals = (short) (localSlot0 + 1);
    minfo.declaredExceptions = new short[0];

    return minfo;
  }


  /*
   * =============== Code Generation Utility Methods ===============
   */

  /*
   * The following methods generate code for the load or store operation
   * indicated by their name for the given local variable.  The code is
   * written to the supplied stream.
   */

  private void code_iload(int lvar, DataOutputStream out)
    throws IOException
  {
    codeLocalLoadStore(lvar, opc_iload, opc_iload_0, out);
  }

  private void code_lload(int lvar, DataOutputStream out)
    throws IOException
  {
    codeLocalLoadStore(lvar, opc_lload, opc_lload_0, out);
  }

  private void code_fload(int lvar, DataOutputStream out)
    throws IOException
  {
    codeLocalLoadStore(lvar, opc_fload, opc_fload_0, out);
  }

  private void code_dload(int lvar, DataOutputStream out)
    throws IOException
  {
    codeLocalLoadStore(lvar, opc_dload, opc_dload_0, out);
  }

  private void code_aload(int lvar, DataOutputStream out)
    throws IOException
  {
    codeLocalLoadStore(lvar, opc_aload, opc_aload_0, out);
  }

//  private void code_istore(int lvar, DataOutputStream out)
//      throws IOException
//  {
//      codeLocalLoadStore(lvar, opc_istore, opc_istore_0, out);
//  }

//  private void code_lstore(int lvar, DataOutputStream out)
//      throws IOException
//  {
//      codeLocalLoadStore(lvar, opc_lstore, opc_lstore_0, out);
//  }

//  private void code_fstore(int lvar, DataOutputStream out)
//      throws IOException
//  {
//      codeLocalLoadStore(lvar, opc_fstore, opc_fstore_0, out);
//  }

//  private void code_dstore(int lvar, DataOutputStream out)
//      throws IOException
//  {
//      codeLocalLoadStore(lvar, opc_dstore, opc_dstore_0, out);
//  }

  private void code_astore(int lvar, DataOutputStream out)
    throws IOException
  {
    codeLocalLoadStore(lvar, opc_astore, opc_astore_0, out);
  }

  /**
   * Generate code for a load or store instruction for the given local
   * variable.  The code is written to the supplied stream.
   *
   * "opcode" indicates the opcode form of the desired load or store
   * instruction that takes an explicit local variable index, and
   * "opcode_0" indicates the corresponding form of the instruction
   * with the implicit index 0.
   */
  private void codeLocalLoadStore(int lvar, int opcode, int opcode_0,
                                  DataOutputStream out)
    throws IOException
  {
    assert lvar >= 0 && lvar <= 0xFFFF;
    if (lvar <= 3) {
      out.writeByte(opcode_0 + lvar);
    } else if (lvar <= 0xFF) {
      out.writeByte(opcode);
      out.writeByte(lvar & 0xFF);
    } else {
      /*
       * Use the "wide" instruction modifier for local variable
       * indexes that do not fit into an unsigned byte.
       */
      out.writeByte(opc_wide);
      out.writeByte(opcode);
      out.writeShort(lvar & 0xFFFF);
    }
  }

  /**
   * Generate code for an "ldc" instruction for the given constant pool
   * index (the "ldc_w" instruction is used if the index does not fit
   * into an unsigned byte).  The code is written to the supplied stream.
   */
  private void code_ldc(int index, DataOutputStream out)
    throws IOException
  {
    assert index >= 0 && index <= 0xFFFF;
    if (index <= 0xFF) {
      out.writeByte(opc_ldc);
      out.writeByte(index & 0xFF);
    } else {
      out.writeByte(opc_ldc_w);
      out.writeShort(index & 0xFFFF);
    }
  }

  /**
   * Generate code to push a constant integer value on to the operand
   * stack, using the "iconst_<i>", "bipush", or "sipush" instructions
   * depending on the size of the value.  The code is written to the
   * supplied stream.
   */
  private void code_ipush(int value, DataOutputStream out)
    throws IOException
  {
    if (value >= -1 && value <= 5) {
      out.writeByte(opc_iconst_0 + value);
    } else if (value >= Byte.MIN_VALUE && value <= Byte.MAX_VALUE) {
      out.writeByte(opc_bipush);
      out.writeByte(value & 0xFF);
    } else if (value >= Short.MIN_VALUE && value <= Short.MAX_VALUE) {
      out.writeByte(opc_sipush);
      out.writeShort(value & 0xFFFF);
    } else {
      throw new AssertionError();
    }
  }

  /**
   * Generate code to invoke the Class.forName with the name of the given
   * class to get its Class object at runtime.  The code is written to
   * the supplied stream.  Note that the code generated by this method
   * may caused the checked ClassNotFoundException to be thrown.
   */
  private void codeClassForName(Class<?> cl, DataOutputStream out)
    throws IOException
  {
    code_ldc(cp.getString(cl.getName()), out);

    out.writeByte(opc_invokestatic);
    out.writeShort(cp.getMethodRef(
      "java/lang/Class",
      "forName", "(Ljava/lang/String;)Ljava/lang/Class;"));
  }


  /*
   * ==================== General Utility Methods ====================
   */

  /**
   * Convert a fully qualified class name that uses '.' as the package
   * separator, the external representation used by the Java language
   * and APIs, to a fully qualified class name that uses '/' as the
   * package separator, the representation used in the class file
   * format (see JVMS section 4.2).
   */
  private static String dotToSlash(String name) {
    return name.replace('.', '/');
  }

  /**
   * Return the "method descriptor" string for a method with the given
   * parameter types and return type.  See JVMS section 4.3.3.
   */
  private static String getMethodDescriptor(Class<?>[] parameterTypes,
                                            Class<?> returnType)
  {
    return getParameterDescriptors(parameterTypes) +
      ((returnType == void.class) ? "V" : getFieldType(returnType));
  }

  /**
   * Return the list of "parameter descriptor" strings enclosed in
   * parentheses corresponding to the given parameter types (in other
   * words, a method descriptor without a return descriptor).  This
   * string is useful for constructing string keys for methods without
   * regard to their return type.
   */
  private static String getParameterDescriptors(Class<?>[] parameterTypes) {
    StringBuilder desc = new StringBuilder("(");
    for (int i = 0; i < parameterTypes.length; i++) {
      desc.append(getFieldType(parameterTypes[i]));
    }
    desc.append(')');
    return desc.toString();
  }

  /**
   * Return the "field type" string for the given type, appropriate for
   * a field descriptor, a parameter descriptor, or a return descriptor
   * other than "void".  See JVMS section 4.3.2.
   */
  private static String getFieldType(Class<?> type) {
    if (type.isPrimitive()) {
      return ProxyGenerator.PrimitiveTypeInfo.get(type).baseTypeString;
    } else if (type.isArray()) {
      /*
       * According to JLS 20.3.2, the getName() method on Class does
       * return the VM type descriptor format for array classes (only);
       * using that should be quicker than the otherwise obvious code:
       *
       *     return "[" + getTypeDescriptor(type.getComponentType());
       */
      return type.getName().replace('.', '/');
    } else {
      return "L" + dotToSlash(type.getName()) + ";";
    }
  }

  /**
   * Returns a human-readable string representing the signature of a
   * method with the given name and parameter types.
   */
  private static String getFriendlyMethodSignature(String name,
                                                   Class<?>[] parameterTypes)
  {
    StringBuilder sig = new StringBuilder(name);
    sig.append('(');
    for (int i = 0; i < parameterTypes.length; i++) {
      if (i > 0) {
        sig.append(',');
      }
      Class<?> parameterType = parameterTypes[i];
      int dimensions = 0;
      while (parameterType.isArray()) {
        parameterType = parameterType.getComponentType();
        dimensions++;
      }
      sig.append(parameterType.getName());
      while (dimensions-- > 0) {
        sig.append("[]");
      }
    }
    sig.append(')');
    return sig.toString();
  }

  /**
   * Return the number of abstract "words", or consecutive local variable
   * indexes, required to contain a value of the given type.  See JVMS
   * section 3.6.1.
   *
   * Note that the original version of the JVMS contained a definition of
   * this abstract notion of a "word" in section 3.4, but that definition
   * was removed for the second edition.
   */
  private static int getWordsPerType(Class<?> type) {
    if (type == long.class || type == double.class) {
      return 2;
    } else {
      return 1;
    }
  }

  /**
   * Add to the given list all of the types in the "from" array that
   * are not already contained in the list and are assignable to at
   * least one of the types in the "with" array.
   *
   * This method is useful for computing the greatest common set of
   * declared exceptions from duplicate methods inherited from
   * different interfaces.
   */
  private static void collectCompatibleTypes(Class<?>[] from,
                                             Class<?>[] with,
                                             List<Class<?>> list)
  {
    for (Class<?> fc: from) {
      if (!list.contains(fc)) {
        for (Class<?> wc: with) {
          if (wc.isAssignableFrom(fc)) {
            list.add(fc);
            break;
          }
        }
      }
    }
  }

  /**
   * Given the exceptions declared in the throws clause of a proxy method,
   * compute the exceptions that need to be caught from the invocation
   * handler's invoke method and rethrown intact in the method's
   * implementation before catching other Throwables and wrapping them
   * in UndeclaredThrowableExceptions.
   *
   * The exceptions to be caught are returned in a List object.  Each
   * exception in the returned list is guaranteed to not be a subclass of
   * any of the other exceptions in the list, so the catch blocks for
   * these exceptions may be generated in any order relative to each other.
   *
   * Error and RuntimeException are each always contained by the returned
   * list (if none of their superclasses are contained), since those
   * unchecked exceptions should always be rethrown intact, and thus their
   * subclasses will never appear in the returned list.
   *
   * The returned List will be empty if java.lang.Throwable is in the
   * given list of declared exceptions, indicating that no exceptions
   * need to be caught.
   */
  private static List<Class<?>> computeUniqueCatchList(Class<?>[] exceptions) {
    List<Class<?>> uniqueList = new ArrayList<>();
    // unique exceptions to catch

    uniqueList.add(Error.class);            // always catch/rethrow these
    uniqueList.add(RuntimeException.class);

    nextException:
    for (Class<?> ex: exceptions) {
      if (ex.isAssignableFrom(Throwable.class)) {
        /*
         * If Throwable is declared to be thrown by the proxy method,
         * then no catch blocks are necessary, because the invoke
         * can, at most, throw Throwable anyway.
         */
        uniqueList.clear();
        break;
      } else if (!Throwable.class.isAssignableFrom(ex)) {
        /*
         * Ignore types that cannot be thrown by the invoke method.
         */
        continue;
      }
      /*
       * Compare this exception against the current list of
       * exceptions that need to be caught:
       */
      for (int j = 0; j < uniqueList.size();) {
        Class<?> ex2 = uniqueList.get(j);
        if (ex2.isAssignableFrom(ex)) {
          /*
           * if a superclass of this exception is already on
           * the list to catch, then ignore this one and continue;
           */
          continue nextException;
        } else if (ex.isAssignableFrom(ex2)) {
          /*
           * if a subclass of this exception is on the list
           * to catch, then remove it;
           */
          uniqueList.remove(j);
        } else {
          j++;        // else continue comparing.
        }
      }
      // This exception is unique (so far): add it to the list to catch.
      uniqueList.add(ex);
    }
    return uniqueList;
  }

  /**
   * A PrimitiveTypeInfo object contains assorted information about
   * a primitive type in its public fields.  The struct for a particular
   * primitive type can be obtained using the static "get" method.
   */
  private static class PrimitiveTypeInfo {

    /** "base type" used in various descriptors (see JVMS section 4.3.2) */
    public String baseTypeString;

    /** name of corresponding wrapper class */
    public String wrapperClassName;

    /** method descriptor for wrapper class "valueOf" factory method */
    public String wrapperValueOfDesc;

    /** name of wrapper class method for retrieving primitive value */
    public String unwrapMethodName;

    /** descriptor of same method */
    public String unwrapMethodDesc;

    private static Map<Class<?>, ProxyGenerator.PrimitiveTypeInfo> table = new HashMap<>();
    static {
      add(byte.class, Byte.class);
      add(char.class, Character.class);
      add(double.class, Double.class);
      add(float.class, Float.class);
      add(int.class, Integer.class);
      add(long.class, Long.class);
      add(short.class, Short.class);
      add(boolean.class, Boolean.class);
    }

    private static void add(Class<?> primitiveClass, Class<?> wrapperClass) {
      table.put(primitiveClass,
        new ProxyGenerator.PrimitiveTypeInfo(primitiveClass, wrapperClass));
    }

    private PrimitiveTypeInfo(Class<?> primitiveClass, Class<?> wrapperClass) {
      assert primitiveClass.isPrimitive();

      baseTypeString =
        Array.newInstance(primitiveClass, 0)
          .getClass().getName().substring(1);
      wrapperClassName = dotToSlash(wrapperClass.getName());
      wrapperValueOfDesc =
        "(" + baseTypeString + ")L" + wrapperClassName + ";";
      unwrapMethodName = primitiveClass.getName() + "Value";
      unwrapMethodDesc = "()" + baseTypeString;
    }

    public static ProxyGenerator.PrimitiveTypeInfo get( Class<?> cl) {
      return table.get(cl);
    }
  }


  /**
   * A ConstantPool object represents the constant pool of a class file
   * being generated.  This representation of a constant pool is designed
   * specifically for use by ProxyGenerator; in particular, it assumes
   * that constant pool entries will not need to be resorted (for example,
   * by their type, as the Java compiler does), so that the final index
   * value can be assigned and used when an entry is first created.
   *
   * Note that new entries cannot be created after the constant pool has
   * been written to a class file.  To prevent such logic errors, a
   * ConstantPool instance can be marked "read only", so that further
   * attempts to add new entries will fail with a runtime exception.
   *
   * See JVMS section 4.4 for more information about the constant pool
   * of a class file.
   */
  private static class ConstantPool {

    /**
     * list of constant pool entries, in constant pool index order.
     *
     * This list is used when writing the constant pool to a stream
     * and for assigning the next index value.  Note that element 0
     * of this list corresponds to constant pool index 1.
     */
    private List<ProxyGenerator.ConstantPool.Entry> pool = new ArrayList<>(32);

    /**
     * maps constant pool data of all types to constant pool indexes.
     *
     * This map is used to look up the index of an existing entry for
     * values of all types.
     */
    private Map<Object,Short> map = new HashMap<>(16);

    /** true if no new constant pool entries may be added */
    private boolean readOnly = false;

    /**
     * Get or assign the index for a CONSTANT_Utf8 entry.
     */
    public short getUtf8(String s) {
      if (s == null) {
        throw new NullPointerException();
      }
      return getValue(s);
    }

    /**
     * Get or assign the index for a CONSTANT_Integer entry.
     */
    public short getInteger(int i) {
      return getValue(new Integer(i));
    }

    /**
     * Get or assign the index for a CONSTANT_Float entry.
     */
    public short getFloat(float f) {
      return getValue(new Float(f));
    }

    /**
     * Get or assign the index for a CONSTANT_Class entry.
     */
    public short getClass(String name) {
      short utf8Index = getUtf8(name);
      return getIndirect(new ProxyGenerator.ConstantPool.IndirectEntry(
        CONSTANT_CLASS, utf8Index));
    }

    /**
     * Get or assign the index for a CONSTANT_String entry.
     */
    public short getString(String s) {
      short utf8Index = getUtf8(s);
      return getIndirect(new ProxyGenerator.ConstantPool.IndirectEntry(
        CONSTANT_STRING, utf8Index));
    }

    /**
     * Get or assign the index for a CONSTANT_FieldRef entry.
     */
    public short getFieldRef(String className,
                             String name, String descriptor)
    {
      short classIndex = getClass(className);
      short nameAndTypeIndex = getNameAndType(name, descriptor);
      return getIndirect(new ProxyGenerator.ConstantPool.IndirectEntry(
        CONSTANT_FIELD, classIndex, nameAndTypeIndex));
    }

    /**
     * Get or assign the index for a CONSTANT_MethodRef entry.
     */
    public short getMethodRef(String className,
                              String name, String descriptor)
    {
      short classIndex = getClass(className);
      short nameAndTypeIndex = getNameAndType(name, descriptor);
      return getIndirect(new ProxyGenerator.ConstantPool.IndirectEntry(
        CONSTANT_METHOD, classIndex, nameAndTypeIndex));
    }

    /**
     * Get or assign the index for a CONSTANT_InterfaceMethodRef entry.
     */
    public short getInterfaceMethodRef(String className, String name,
                                       String descriptor)
    {
      short classIndex = getClass(className);
      short nameAndTypeIndex = getNameAndType(name, descriptor);
      return getIndirect(new ProxyGenerator.ConstantPool.IndirectEntry(
        CONSTANT_INTERFACEMETHOD, classIndex, nameAndTypeIndex));
    }

    /**
     * Get or assign the index for a CONSTANT_NameAndType entry.
     */
    public short getNameAndType(String name, String descriptor) {
      short nameIndex = getUtf8(name);
      short descriptorIndex = getUtf8(descriptor);
      return getIndirect(new ProxyGenerator.ConstantPool.IndirectEntry(
        CONSTANT_NAMEANDTYPE, nameIndex, descriptorIndex));
    }

    /**
     * Set this ConstantPool instance to be "read only".
     *
     * After this method has been called, further requests to get
     * an index for a non-existent entry will cause an InternalError
     * to be thrown instead of creating of the entry.
     */
    public void setReadOnly() {
      readOnly = true;
    }

    /**
     * Write this constant pool to a stream as part of
     * the class file format.
     *
     * This consists of writing the "constant_pool_count" and
     * "constant_pool[]" items of the "ClassFile" structure, as
     * described in JVMS section 4.1.
     */
    public void write(OutputStream out) throws IOException {
      DataOutputStream dataOut = new DataOutputStream(out);

      // constant_pool_count: number of entries plus one
      dataOut.writeShort(pool.size() + 1);

      for ( ProxyGenerator.ConstantPool.Entry e : pool) {
        e.write(dataOut);
      }
    }

    /**
     * Add a new constant pool entry and return its index.
     */
    private short addEntry( ProxyGenerator.ConstantPool.Entry entry) {
      pool.add(entry);
      /*
       * Note that this way of determining the index of the
       * added entry is wrong if this pool supports
       * CONSTANT_Long or CONSTANT_Double entries.
       */
      if (pool.size() >= 65535) {
        throw new IllegalArgumentException(
          "constant pool size limit exceeded");
      }
      return (short) pool.size();
    }

    /**
     * Get or assign the index for an entry of a type that contains
     * a direct value.  The type of the given object determines the
     * type of the desired entry as follows:
     *
     *      java.lang.String        CONSTANT_Utf8
     *      java.lang.Integer       CONSTANT_Integer
     *      java.lang.Float         CONSTANT_Float
     *      java.lang.Long          CONSTANT_Long
     *      java.lang.Double        CONSTANT_DOUBLE
     */
    private short getValue(Object key) {
      Short index = map.get(key);
      if (index != null) {
        return index.shortValue();
      } else {
        if (readOnly) {
          throw new InternalError(
            "late constant pool addition: " + key);
        }
        short i = addEntry(new ProxyGenerator.ConstantPool.ValueEntry(key));
        map.put(key, new Short(i));
        return i;
      }
    }

    /**
     * Get or assign the index for an entry of a type that contains
     * references to other constant pool entries.
     */
    private short getIndirect( ProxyGenerator.ConstantPool.IndirectEntry e) {
      Short index = map.get(e);
      if (index != null) {
        return index.shortValue();
      } else {
        if (readOnly) {
          throw new InternalError("late constant pool addition");
        }
        short i = addEntry(e);
        map.put(e, new Short(i));
        return i;
      }
    }

    /**
     * Entry is the abstact superclass of all constant pool entry types
     * that can be stored in the "pool" list; its purpose is to define a
     * common method for writing constant pool entries to a class file.
     */
    private static abstract class Entry {
      public abstract void write(DataOutputStream out)
        throws IOException;
    }

    /**
     * ValueEntry represents a constant pool entry of a type that
     * contains a direct value (see the comments for the "getValue"
     * method for a list of such types).
     *
     * ValueEntry objects are not used as keys for their entries in the
     * Map "map", so no useful hashCode or equals methods are defined.
     */
    private static class ValueEntry extends ProxyGenerator.ConstantPool.Entry
    {
      private Object value;

      public ValueEntry(Object value) {
        this.value = value;
      }

      public void write(DataOutputStream out) throws IOException {
        if (value instanceof String) {
          out.writeByte(CONSTANT_UTF8);
          out.writeUTF((String) value);
        } else if (value instanceof Integer) {
          out.writeByte(CONSTANT_INTEGER);
          out.writeInt(((Integer) value).intValue());
        } else if (value instanceof Float) {
          out.writeByte(CONSTANT_FLOAT);
          out.writeFloat(((Float) value).floatValue());
        } else if (value instanceof Long) {
          out.writeByte(CONSTANT_LONG);
          out.writeLong(((Long) value).longValue());
        } else if (value instanceof Double) {
          out.writeDouble(CONSTANT_DOUBLE);
          out.writeDouble(((Double) value).doubleValue());
        } else {
          throw new InternalError("bogus value entry: " + value);
        }
      }
    }

    /**
     * IndirectEntry represents a constant pool entry of a type that
     * references other constant pool entries, i.e., the following types:
     *
     *      CONSTANT_Class, CONSTANT_String, CONSTANT_Fieldref,
     *      CONSTANT_Methodref, CONSTANT_InterfaceMethodref, and
     *      CONSTANT_NameAndType.
     *
     * Each of these entry types contains either one or two indexes of
     * other constant pool entries.
     *
     * IndirectEntry objects are used as the keys for their entries in
     * the Map "map", so the hashCode and equals methods are overridden
     * to allow matching.
     */
    private static class IndirectEntry extends ProxyGenerator.ConstantPool.Entry
    {
      private int tag;
      private short index0;
      private short index1;

      /**
       * Construct an IndirectEntry for a constant pool entry type
       * that contains one index of another entry.
       */
      public IndirectEntry(int tag, short index) {
        this.tag = tag;
        this.index0 = index;
        this.index1 = 0;
      }

      /**
       * Construct an IndirectEntry for a constant pool entry type
       * that contains two indexes for other entries.
       */
      public IndirectEntry(int tag, short index0, short index1) {
        this.tag = tag;
        this.index0 = index0;
        this.index1 = index1;
      }

      public void write(DataOutputStream out) throws IOException {
        out.writeByte(tag);
        out.writeShort(index0);
        /*
         * If this entry type contains two indexes, write
         * out the second, too.
         */
        if (tag == CONSTANT_FIELD ||
          tag == CONSTANT_METHOD ||
          tag == CONSTANT_INTERFACEMETHOD ||
          tag == CONSTANT_NAMEANDTYPE)
        {
          out.writeShort(index1);
        }
      }

      public int hashCode() {
        return tag + index0 + index1;
      }

      public boolean equals(Object obj) {
        if (obj instanceof ProxyGenerator.ConstantPool.IndirectEntry ) {
          ProxyGenerator.ConstantPool.IndirectEntry other = (ProxyGenerator.ConstantPool.IndirectEntry) obj;
          if (tag == other.tag &&
            index0 == other.index0 && index1 == other.index1)
          {
            return true;
          }
        }
        return false;
      }
    }
  }
}
